So-called “blank” ammunition consists of shell casings loaded with gun power or other explosive but without projectiles. When fired, a blank round sounds much like “live” ammunition but, unlike live ammunition, no projectile leaves the barrel of the gun in which the blank was fired. Blank ammunition is used extensively in military training for safety reasons.
In the case of a gas operated automatic rifle or machine gun a portion of the gas pressure created inside a gun's barrel by the ignition of a cartridge is diverted through a small hole in the barrel to be utilized for the operation of the gun's mechanism that ejects the spent cartridge case and loads a live one from the gun's magazine. In the case of the firing of a “blank” there is less gas pressure built up in the barrel because there is no projectile being forced through the barrel. The lower gas pressure in the barrel causes the diverted gas to be of too low a pressure to properly operate the gun's ejection and loading mechanism. Typically, an adapter is fitted onto the end of the barrel that restricts the flow of gas and increases the pressure in the barrel to a level that equals the pressure created when a “live” cartridge is fired. Thus the adapter allows a gun firing blank ammunition to operate in the same way as the gun would when firing “live” ammunition.
Existing blank adapters were designed to work with older model machine guns such as the M240, which normally operate under moderate firing schedules. There is a significant and adverse impact on the life of the older design of the blank firing adapter when used on newer, shorter and lighter weight machine guns, such as the Mark 48. The newer, lighter guns operate at accelerated firing schedules and are configured with shorter and lighter barrels, which create increased temperatures. The increased temperatures seen at the muzzle of newer lightweight guns damage the blank adapter made to the older design. The temperatures developed at the muzzle end of the barrel exceed the design parameters for the older blank firing adapter and consequentially reduce its life from 7,000 rounds to 500 rounds. This diminution of blank firing adapter life is unacceptable for its use on a new type machine gun.
Another problem with blank firing adapters is that as the muzzle end of the barrel heats up, the blank firing adapter heats unevenly, causing the adapter to loosen. When the adapter loosens, gas escapes around the tapered end of the stem, causing a reduction in pressure inside the barrel and damage to the adapter. The reduction in pressure consequently reduces the amount of diverted gas below the level required for the proper operation of the gun's mechanism. When it loosens the operator must stop and re-tighten the adapter using a special tool. Typically, re-tightening the existing adapter on an older style gun is required around 1,000 rounds. For a new style gun it is required almost immediately.